Normalized-Full-Scale-Referencing Digital-Domain Linearity Calibration for SAR ADC

Abstract

This paper proposes a linearity calibration algorithm of a capacitive digital-to-analog converter (CDAC) for successive approximation register (SAR) analog-to-digital converters (ADCs) based on a normalized-full-scale of the DAC. Since the capacitor weight errors are represented as the difference between the real and ideal weights with respect to the normalized-full-scale, the calibrated digital representation of CDAC does not have gain error. A model of a 14-bit-format SAR ADC with a segmented CDAC by a bridge capacitor is simulated to demonstrate the performance of the proposed calibration algorithm. The effective number of bits (ENOB) and spurious-free dynamic range (SFDR) of the 14-bit-format ADC model are improved to 13.2 bits and 94.0 dB from 8.4 bits and 54.8 dB, respectively, at a standard deviation of a unit capacitor of 2%. The gain-error-free characteristic of the proposed linearity calibration algorithm is verified with a 2-channel time-interleaved (TI) SAR ADC model.